1. Field of the Invention
The present invention generally relates to repair or circuit modification of microelectronic chips particularly during manufacture. More specifically, chips having conductors, typically copper or aluminum, embedded in organic dielectric layers can be modified after the conductors have been formed. This organic dielectric layer is also variously described in the art by terminology such as low-k dielectric, spin-on glass, or spin-on dielectric.
2. Description of the Related Art
The Focused Ion Beam (FIB) tool is well known in the art for ion milling and has been used for chip analysis, modification, and repair. A typical conventional system utilizes bromine gas and a focused ion beam to selectively mill aluminum lines in a silicon oxide dielectric, a procedure that slices through the conductor to create an electrical open circuit. The complementary procedure of adding conductive material to create shorts or to connect two conductors is done by ion-assisted deposition of a metal such as tungsten from a gaseous metal precursor onto the area to be connected. This conventional method of creating electrical disconnections is not applicable to organic dielectric/metallization schemes because no gas is commercially available that ensures the complete removal of residual metal, such as copper, in the milled area. More important, ion milling utilizes charged ions that impregnate the organic dielectric to defeat electrical isolation.
Conventional methods using FIB milling concern aluminum lines in silicon oxide and does not work for tight pitch copper lines in low-k dielectric materials. Thus, until now no effective method exists to allow circuit modification of chips with organic dielectric layers. The disclosed technique overcomes the above mentioned problems of charged ions and residual metal by using a combination of selective dielectric removal and FIB milling.
In view of the foregoing and other problems of the conventional methods, it is, therefore, an object of the present invention to provide a method for repairing metal lines in low-k organic dielectrics.
It is another object of the invention to allow real-time circuit modifications on-chip on such chips when a circuit design change needs to be evaluated or a mask error needs to be corrected.
It is another object of the invention to allow conductor lines in low-k organic dielectrics to be selectively disconnected or selectively connected.
It is another object of the invention to improve yields on such chips, especially on large area chips where chip interconnect problems can be a major yield detractor.
It is another object of the invention to allow repairs on chips having organic dielectric/metal combinations, especially when conductor lines are closely spaced.
In a first exemplary aspect, a method for making an organic dielectric/copper modification involves: depositing an inorganic dielectric material such as nitride to form a surface protective layer; making an opening above the selected work area through this protective layer either by ion milling or by a standard mask/resist process; removing organic dielectric material adjacent to the targeted copper line by an oxygen Reactive Ion Etching (RIE) process; and, modifying the exposed conductor by either cutting the copper line by FIB milling (typically with a passivating gas such as xenon diflouride) or by depositing more conductive material to form a connection to another conductor. Repairs would normally be followed by routine deposition of an insulating layer such as silicon oxide to fill in the void of the removed organic dielectric and then a planarization process to equalize surface contours. Repairs of underlying conductors can be done by executing the basic process for each successive underlying dielectric layer.
With the invention, the problem in the prior art is overcome in which ion milling creates charged ions that impregnate the organic dielectric to defeat electrical isolation. The invention also overcomes the problem in the prior art of electrically conductive metal residue from ion milling being deposited on the sidewalls around the milled area, defeating electrical isolation.